1. Field of the Invention
The present invention relates to a radar apparatus.
2. Description of the Related Art
An automotive radar using millimeter wave, or a high-frequency radio communication apparatus and radio terminal using waves in a frequency band of 300 MHz or above contain a single multifunctional semiconductor device, a semiconductor integrated circuit (IC), an IC package which packages the ICs, a plurality of interconnected ICs or a high-frequency circuit element having a filter function in a housing. This is for the miniaturization, and cost reduction of the apparatuses, and to cope with multi-functionalization of the circuit element to be used.
When packing many functional devices in one housing structure, if the size of the housing remains constant and the number of the functional devices increases, the physical distance between the functional devices will be decreased correspondingly, or the size of the housing will be larger than half the free-space wavelength at a signal frequency (for example, about 1.95 mm at 77 GHz). In either case, radio energy of a signal frequency radiated from one point of IC or the like constituting a functional device within the housing is easily dissipated in the housing, and combines with a functional device within the same housing, thus causing various functional troubles. For example, if part of signals emitted from a transmission function device into the housing is coupled with a reception functional device, a communication transmitter-receiver or a transmitter-receiver module for automotive millimeter wave radar experiences a trouble such as the saturation of a receiver, an increase in received noise or the like.
To cope with these problems, especially an interference problem in the housing, a conventional communication apparatus has divided the housing structure into a plurality of small rooms by metal partitions, or has provided a metal structure along a conventional communication path that serves as a cutoff waveguide structure for locally cutting off unnecessary irradiation. These conventional techniques require a complicated metal structure for the housing structure, and a division of high-frequency board of a passive circuit into a plurality of parts. Further, these structures and the division of the high-frequency board into a plurality of parts make the arrangement of semiconductor ICs and the passive circuit components more difficult, thus inhibiting mass production and cost reduction of the communication apparatus.
JP-A-2000-307305 is among the conventional techniques for solving there problems.
However, while the prevention in JP-A-2000-307305 proposes a mounting configuration in which a filter has a lid formed with projections by extrusion press, the invention does not refer to a relative positional relationship between the projections and the high-frequency circuit elements or passive components, and an optimal configuration of the projections on those positions.
However, a dielectric resonator is generally used as an oscillator which is a high-frequency circuit element. Oscillation frequency of the oscillator changes a lot depending on the dielectric resonator and electric field conditions in the vicinity of the dielectric resonator. Thus, if there exist projections which are extrusion-pressed on the lid in the vicinity of the dielectric resonator, the oscillation frequency changes a lot depending on the shape and position of the projections, thereby making it very difficult to acquire a desired oscillation frequency.
Since the projections are formed by press working, if the projections diminish in size, increase in height, or increase in number, pressing load is increased and thus the life of a press mold will be shortened. Therefore, it is necessary to arrange projections of optimal shape and height only at required places on the lid.
It is an object of the present invention to provide a filter cover that has little electromagnetic effect on the dielectric resonator and is able to lengthen the life of the press mold without injuring isolation between transmission and reception.